This invention relates to a lubricating system for turbo-chargers and more particularly to an improved lubricating system that insures against damage to the drive bearings of a supercharger upon stopping and subsequent restarting of the associated engine.
The use of superchargers as a device for inreasing the power output of an engine is well known. These devices, particularly those of the centrifugal type, rotate at extremely high speeds. In many applications it is not uncommon for the impeller and its driving shaft to rotate at speeds of in excess of 100,000 rpm. With such high rotational speeds it is important that the supporting bearings of the impeller and its drive shaft receive adequate lubrication and, for this reason, it has been the general practice to provide pressure lubrication for the bearings.
When the supercharger is of the turbo-charged type (the compressor is driven by an exhaust gas driven turbine) still additional problems are encountered. The turbine stage of a turbo-charger operates at relatively high temperatures. When the engine stops running, the residual heat in the turbo-charger acts upon the lubricant remaining on the bearing surfaces and can cause thermal deterioration of the lubricant. In fact the heat may be sufficient so as to cause the lubricant to carbonize on the bearings. Thus, upon subsequent restarting of the engine there can be significant damage to the bearings due to improper lubrication and the retention of the carbonized material in the bearing surfaces. In order to prevent these difficulties, it has been proposed to embody an arrangement wherein even though the engine is switched off, it is operated under a idle mode for a period of time so as to permit cooling of the bearings. Alternatively, it has been proposed to control the engine on restarting so that it will not be driven faster than its idle speed for a certain period of time to insure removal of the thermally degraded oil and other deposits before the engine can be operated at high speeds. Of course, such arrangements are not only expensive but are objectionable to the operator.
It is, therefore, a principal object of this invention to provide an improved lubricating system for an engine supercharger.
It is another object of this invention to provide an improved turbo-charger lubricating system.
It is yet a further object of this invention to provide a lubricating system for a supercharger wherein the bearings are supplied with oil after the engine is stopped.